WO2005108920A1

WO2005108920A1 - Target acquisition device

Info

Publication number: WO2005108920A1
Application number: PCT/EP2005/004618
Authority: WO
Inventors: Jürg HINDERLING
Original assignee: Leica Geosystems Ag
Priority date: 2004-05-04
Filing date: 2005-04-29
Publication date: 2005-11-17
Also published as: EP1743139B1; US7826039B2; EP1743139A1; DE502005009867D1; JP2007536537A; US20080062526A1; ATE473420T1

Abstract

The invention relates a target acquisition device, wherein attenuating filters (18; 19) are mounted upstream and downstream of a receiver (2) and a transmitter (1), respectively, in order to specifically attenuate radiation portions that originate from zigzag reflections. Said filters attenuate radiation by an intensity of at least a factor of 0.7, preferably at least 0.5 or 0.3. Alternatively or additionally thereto, deflection devices such as a mirror (10) or a cubic prism (14) can be configured so as to attenuate radiation. Since zigzag reflected radiation portions pass through the attenuating devices at least twice as often as regular radiation portions, they are attenuated to a correspondingly higher extent. The entrance surface (5) of the receiver can also be surrounded by a conical deflection surface which substantially absorbs any incident light and reflects the rest to directions different from that of the direction of incidence so that no zigzag reflections can occur.

Description

DESCRIPTION

GO DETECTING DEVICE

Technical field

The invention relates to a target acquisition device according to the preamble of claim 1, e.g. an optoelectronic range finder or direction meter. With such a target detection device, parameters of the position of a target with respect to that of the device, such as its distance or the direction in which it is located, can be determined by illuminating it with a modulated light beam and processing the collected radiation reflected by it. Target acquisition devices of this type are mainly used for surveying purposes. Typical targets are retroreflectors made of glass or reflective foils made of plastic. State of the art

Generic target acquisition devices are known from numerous publications. In the range finder described in DE 198 40 049 AI, a combined transmission beam is deflected into the optical axis of the single objective and the measurement beam received by the same is processed by determining its transit time or phase and deriving the distance from the target.

A similar range finder is known from DE 43 16 348 AI, in which the transmitter is assigned its own lens, which is separate from that of the receiver.

With target acquisition devices of this type, multiple reflections occur, in which portions of the measurement reflected from the target Reflected on elements of the device and superimposed on the transmission beam, so that a part of it is reflected a second time at the target and then collected by the receiver. Those parts that pass through the path from the target acquisition device to the target and back twice or even more often with multiple reflections on the device can cause disturbing falsifications, especially if the processing of the measuring beam is based on the determination of its phase, running time or image to determine the direction cause the measurement result. In general, the greater the relative intensity of the multi-reflected portion, the greater these. They are therefore particularly important when the distance between the target acquisition device and the target is small, if the intensity of the multiply reflected components is relatively high despite the attenuations occurring during the reflections.

Reflections on the receiver are particularly critical, in particular on the entrance surface of the same or on surfaces surrounding it, but disturbing reflections can also occur on the transmitter. In both cases, the optics bundle reflected radiation to a greater or lesser extent onto the target and therefore weaken it only slightly, so that the measurement result can be noticeably falsified.

There are also methods for distance measurement in which multiple reflections do not influence the measurement result, for example the zero phase adjustment used in the applicant's Meko eter ME 5000, in which the modulation frequency is adjusted so that the path between transmitter and receiver on the one hand and destination on the other hand always is a multiple of the modulation wavelength, but the use of such methods is generally complex and the corresponding target acquisition devices are relatively large and expensive. Presentation of the invention

The invention is based on the object of improving a generic target detection device with regard to its measuring accuracy by suppressing multiple reflections between the target object and the instrument as far as possible. This object is achieved by the features in the characterizing part of claim 1. Alternative and preferred embodiments of the invention are described in the characteristics of the dependent claims.

The invention provides a target detection device in which radiation which originates from multiple reflections, especially those at the receiver or at the transmitter, or which could lead to such, is suppressed as far as possible or specifically weakened. In this way, the measurement errors caused by multiple reflections are largely eliminated or significantly reduced.

Brief description of the drawings

The invention is explained in more detail below with reference to figures which merely represent exemplary embodiments. Show it

1 schematically shows the structure of a range finder according to the invention,

2 shows a section through part of the receiver of the range finder of FIG. 1,

Fig. 3 shows schematically the structure of a direction meter according to the invention and FIG. 4 is a front view of part of the receiver of the direction meter of FIG. 3.

Ways of Carrying Out the Invention

The rangefinder shown in FIG. 1 has a transmitter 1 and a receiver 2 in a housing, which comprises a holder 3 and an optical fiber 4 which is fastened to the holder 3 and whose end face forms a coated entry face 5. It leads to a light-sensitive element which generates an electrical measurement signal corresponding to the intensity of the incident light, e.g. a photodiode 6. The transmitter 1 comprises a e.g. Laser diode 7 transmitting in the infrared range and a collimation optics 8 arranged downstream thereof. The laser diode 7 is controlled by a control unit 9, which also processes the output signal of the photodiode 6.

The beam coming from the transmitter 1 is deflected by a mirror 10 as the first deflecting means into the optical axis of an objective 11, through which it is transmitted as a transmitting beam 12 with i.a. low beam expansion is directed against a target 13 which is designed as a retroreflector, reflector foil or cat's eyes or from the surface of any object, e.g. of a building.

A little behind the mirror 10, a second deflection element is arranged in the optical axis of the objective 11, which is designed as a cube prism 14. It directs the measuring beam 15 incident through the objective 10, ie essentially the portion of the transmitted beam 12 reflected by the target 13, against the entry surface 5 of the receiver 2. A reference light path of known length is produced by two beam splitters 16, 17, the first of which lies between the collimating optics 8 and the mirror 10 and the second between the cube prism 14 and the entrance surface 5, via which part of the light emitted by the transmitter 1 is produced

Beam is fed directly to the receiver 2 as a reference beam.

Measuring beam 15 and reference beam can partly be reflected at the receiver 2. In addition, a portion of the measuring beam 15 can also reach the transmitter 1 and be reflected on it. After reflection on target 13, these components can cause the measurement result to be falsified.

For the targeted weakening of rays that originate from multiple reflections, the entrance surface 5 of the receiver 2 is immediately connected upstream of a first attenuation filter 18, which weakens transmitted light, i.e. its intensity is reduced by a factor A for which e.g. A≤0.7, preferably A≤O .5 or even A≤0.3 applies.

A corresponding second attenuation filter 19 is arranged directly after the collimation optics 8 of the transmitter 1. The two attenuation filters 18, 19 can be designed to be switchable, so that they can be connected upstream or downstream of the receiver 2 or the transmitter 1, preferably independently of one another, in particular depending on the magnitude of the distance from the target 13, so that the attenuation filters 18, 19 or at least one of them can be dispensed with for larger distances. The attenuation filters 18, 19 can also have a transmittance that can be adjusted or adjusted, so that the extent of the attenuation is selected depending on the distance from the target can be. Otherwise, the attenuation filters 18, 19 can each be designed in different ways, for example as panchromatic or orthochromatic film material or as orthochromatically sensitized X-ray film, as neutral filter or gelatin gray filter or as transparent film or as glass with line structure such as raster filter, grid filter or filter with stochastic weakening pattern.

Alternatively or additionally, however, the first and / or the second deflection means can also be designed as a weakening means. For example, the mirror 10 can be designed as a dichroic mirror, which absorbs part of the light that falls on it. Likewise, the cube prism 14 can be designed to be slightly absorbent.

A deflection surface 20 is provided on the holder 3 of the receiver 2 as a further attenuation means for beam components that could give rise to multiple reflections. It forms a 0.5 mm to 1.5 mm deep, essentially conical, conical funnel, in the axis of which an approximately equally long end section 21 of the optical fiber 4, which adjoins the entry surface 5, is exposed. Alternatively, this deflection surface could also be designed as a conically raised surface surrounding the optical fiber 4. The conical shape is exemplary of a surface shape that reflects the measuring beams falling on it in a direction that deviates from their direction of incidence.

To measure the distance of the target 13 from the range finder, a sequence of short light pulses can be emitted by the transmitter 1 and the distance from the transit time until the arrival of the pulses reflected by the target 13 can be determined, or a continuous light beam can be emitted periodically, e.g. with a sine that is modulated. In the latter case, the phase position of the beam reflected by the target and received by the receiver 2 relative to the reference beam is determined to determine the distance. These methods are well known and will not be explained in more detail here.

Especially in phase measurement, beam components play which do not cover the regular light path from the transmitter 1 via the mirror 10, the lens 11 to the target 13 and back through the lens 11 and via the cube prism 14 into the optical fiber 4, but also on another object are reflected as the target 13 and thus cover part of the way twice or more, a role that is not always negligible. The reflection of a portion of the measurement beam 15 reflected by the target 13 and incident through the objective 11 at the receiver 2, in particular at its entry surface 5, is particularly critical. by 5%, but this has the disadvantage that the measuring beam is refracted so that it enters at an angle. This reduces the usable numerical aperture of the fiber.

According to the invention, as described, reflected beam components are specifically weakened by the attenuation filter 18. The regular beam component, ie reflected only once at the target 13, passes through the attenuation filter 18 only once and is therefore weakened by the factor A only once. On the other hand, a portion reflected at the entrance surface 5, which is reflected again at the target 13, runs the attenuation filter 18 three times, that is, it is weakened by a factor A ³ , that is, it is weakened by a factor A ² , that is to say around 0.3 at A = 0.3 ^2s «0.1 more weakened and thus almost completely suppressed compared to the regular portion, especially since the reflection at the entrance surface 5 and is connected to a weakening at the target 13, to which the twice reflected portion is tripled, but the regular portion is only subjected to one.

Parts of the measuring beam 15 that fall on the surroundings of the entrance surface 5 can also be disruptive. Here, the design of the deflection surface 20 ensures that a larger portion is absorbed and the rest, which can never be completely avoided, is reflected in a direction that does not correspond to the direction of incidence, so that it does not cross the cube prism 14 and the objective 10 against the target 13 is reflected. The mentioned designs of the deflection surface 20 bring about a substantial reduction in disturbing reflections at the receiver 2 and can also be provided by themselves as a measure to reduce multiple reflections.

The attenuation filter 19 plays a role which corresponds to that of the attenuation filter 18 for beam portions reflected by the receiver 2, for portions of the measurement beam 15 which are reflected back onto the transmitter 1 via the mirror 10 and reflected on the same. Here, too, there is a threefold reduction compared to a simple one of the regular beam component. A total of at least three variants of range finders are conceivable, one with only one attenuating means 18 in front of the receiver, another with only one attenuating means 19 in front of the transmitter, and furthermore one with two attenuating means 18 and 19 according to FIG. 1.

As mentioned, it is also possible to integrate the attenuating means with the deflecting means - whether it is a mirror, a prism or another component that deflects the beam path. Above all, this simplifies the construction of the rangefinder and reduces the cost of its manufacture. development. In addition, hardly any disturbing reflections can arise from a dichroic mirror. If the attenuation means are designed as attenuation filters arranged as close as possible to the transmitter and / or the receiver, then practically all internal reflections, apart from any reflections on the attenuation filters themselves, are attenuated. In this way, portions reflected in the reference light path, which can also falsify the measurement result, are weakened.

The range finder shown in FIGS. 1, 2 is - as is known to the person skilled in the field of distance measurement - only one of several possibilities for arranging the essential components. The principle according to the invention for suppressing or reducing multiple reflections which negatively influence the measuring accuracy is the same

Way applicable both with coaxial rangefinders with one or two lenses and with non-coaxial rangefinders.

Corresponding considerations also apply to the directional meter which can be seen in FIGS. 3, 4. This device is partly like the range finder shown in FIGS. 1, 2. Corresponding parts have the same names and are not described again to avoid repetition.

The receiver 2 lies in the optical axis and is designed as an electronic camera with, for example, a rectangular screen 22 made of light-sensitive elements such as CCD or CMOS, the center of the screen being at or near the focal point of the lens 11. A first attenuation filter 18 is in turn connected upstream of the receiver 2 and a second attenuation filter 19 is connected downstream of the transmitter 2. The target 13 is designed as a reflector, in particular as a triple prism.

The measuring beam 15, generated by the preferably divergent transmission beam 12 reflected at the target 13, is collimated onto a measuring light spot 23 on the screen 22, the position of which depends on the direction which the direction in which the target 13 lies with the optical axis of the device. Multiple reflections can lead to portions of the measurement beam 15 falling on the screen 22 in the vicinity of the measurement light spot 23 and causing so-called ghost images, which make it difficult to determine the position of the measurement light spot 23 exactly. Double or multiple images are particularly likely due to reflections on the large-area screen 22. Part of the radiation from the light spot 23 is reflected back via the lens 11 in the direction of the target 13, reflected by the latter again and imaged again on the screen 22 as a ghost image. These unwanted ghost images are also larger than the actual measuring light spot due to the lack of focus. The measures according to the invention, in particular the first attenuation filter 18 but also the second attenuation filter 19, in turn weaken these multiple reflections to such an extent that they have no distorting influence on the measurement result.

Claims

PAT EN TAN SP RÜ CHE

1. Target acquisition device with a lens (11), an electrically controllable transmitter (1) for transmitting a transmission beam (12), a receiver (2) for receiving a measuring beam (15) from portions of the transmission beam reflected from a target (13) (12) through the lens (11), with the same downstream screen (22) or the same downstream entrance surface (5) and a light-sensitive element connected to it, possibly light-conducting, which generates an electrical measurement signal when light falls, and with a control device (9) for controlling the transmitter (1) and processing the measurement signal, characterized in that it has attenuation means for the targeted suppression or attenuation of rays that originate from multiple reflections or could give rise to multiple reflections.

2. Target detection device according to claim 1, characterized in that the attenuation means comprise at least a first attenuation means, which is arranged upstream of the receiver (2) and reduces the intensity of a beam guided over the same.

3. Target detection device according to claim 2, characterized in that the at least one first attenuation means is designed such that the intensity of a beam guided over the same is reduced by a factor of ≤0.7, preferably ≤0 .5 and in particular ≤O .3.

4. Target acquisition device according to claim 2 or 3, characterized in that the at least one first weakening is designed as an attenuation filter (18).

5. Target detection device according to one of claims 2 to 4, characterized in that it comprises a first deflection means for deflecting the measuring beam (15) incident through the objective (11).

6. Target acquisition device according to claim 5, characterized in that the at least one first attenuation means is integrated with the first deflection means.

7. Target detection device according to claim 6, characterized in that the first deflecting means is an absorbing cube prism (14) or a dichroic mirror.

8. Target detection device, in particular according to one of claims 1 to 7, characterized in that the weakening means comprise a deflection surface (20) which at least partially surrounds the entrance surface (5) of the receiver (2) and incident portions of the measuring beam (15) insofar as they are not absorbed, mainly reflected in directions that deviate from the direction of incidence.

9. Target detection device according to claim 8, characterized in that the deflecting surface (20) has the shape of a, preferably conical, funnel.

10. Target acquisition device according to claim 9, characterized in that the funnel has a depth of between 0.5 mm and 1.5 mm and the entry surface (5) is formed by the end surface of a light guide (4), whose end section (21) surrounds the funnel at a distance.

11. Target detection device according to one of claims 8 to 10, characterized in that the deflecting surface (20) is designed to be absorbent.

12. Target detection device according to one of claims 1 to 11, characterized in that the attenuation means comprise at least one second attenuation means, which is arranged downstream of the transmitter and reduces the intensity of a beam guided over the same.

13. Target detection device according to claim 12, characterized in that the at least one second attenuation means is designed such that the intensity of a beam guided over the same is reduced by a factor of ≤0.7, preferably ≤0.5 and in particular ≤0.3.

14. Target acquisition device according to claim 12 or 13, characterized in that the at least one second attenuation means is designed as an attenuation filter (19).

15. Target acquisition device according to claim 14, characterized in that it comprises a beam splitter (16) downstream of the attenuation filter (19), which branches off a reference beam from the beam emitted by the transmitter (1).

16. Target acquisition device according to one of claims 12 to 15, characterized in that it has a second deflecting includes tel for deflecting the transmission beam (12) against the lens (11).

17. Target acquisition device according to claim 16, characterized in that the at least one second weakening means is integrated with the second deflection means.

18. Target detection device according to claim 17, characterized in that the second deflection means is an absorbing cube prism or a dichroic mirror (lθ).

19. Target acquisition device according to claim 4 or claim 14, characterized in that the first attenuation filter (18) and / or the second attenuation filter (19) is switchable and / or has an adjustable transmittance, so that the extent of the attenuation is adjustable.

20. Target acquisition device according to claim 4, claim 14 or claim 20, characterized in that the first attenuation filter (18) and / or the second attenuation filter (19) as panchromatic or orthochromatic film material or orthochromatically sensitized X-ray film, as a neutral filter or gelatin - Gray filter or transparent film or as glass with a line structure such as raster filter, grating filter or filter with stochastic weakening pattern.